The last time a Nato summit was held in the UK, Margaret Thatcher was in the chair in London. It was 1990. The Cold War had been won.

A Europe "whole and free" was mentioned in the communique, alongside how "the Soviet Union has embarked on the long journey toward a free society".

Today, relations between Moscow and the West are at their lowest ebb since the Cold War.

And another Conservative prime minister, David Cameron, will chair a Nato summit, talking of a new threat that will require a generational ideological struggle "not unlike the Cold War" - against the self-declared Islamic State.

All of this speaks to a new world disorder. There's political chaos in Pakistan, Afghanistan is hardly stable, and the world has taken its eyes away from an extraordinary war in Libya.

At Celtic Manor in Wales, the talk will be about a new era of co-operation between Europe, the US and new partners.

The Ukraine crisis and the Islamic State are expected to top the agenda

Armoured personnel carriers, tanks and interactive defence displays will be parked on the fairways. There will be fly-pasts of Nato air assets. The Government rarely misses an opportunity to try and boost exports.

What both the PM and President Obama have referred to as "Russia's aggression" in Ukraine, and the threat from IS, will dominate the talks, even if the latter is only scheduled to be discussed at dinner on Friday night.

Video:Prime Minister On IS Threat

On Russia, the post-Cold War vision of a Europe whole and free is now being challenged by the actions of President Putin.

It seems a drastic step, but Nato may effectively alter the "founding act" of its relationship with Russia, essentially a promise not to build permanent bases in Eastern Europe.

The Baltic states and Poland would like this revisited. Germany, closer to Russia than the rest of Europe, is pushing back.

Video:Ukraine And Iraq To Top Nato Talks

Officially, the founding act will stay. But expect new forward bases in Eastern Europe to allow rapid reaction to President Putin's "hybrid war" - the rapid use of deniable Russian military assets, known locally as "little green men".

President Poroshenko will meet with the "quint" (the US, UK, France, Germany and Italy) just before the summit. France has already paused the highly controversial sale of Mistral helicopter carriers. The export was due within weeks.

On IS, we are seeing the ramping of rhetoric to levels consistent with a more concerted military effort. President Obama said he wanted to destroy and degrade IS.

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Gallery: The History Of Nato's Expansion

The summit will be about slow coalition building on the margins. Alongside 28 Nato leaders, including Turkey, there will be allies and partners such as Jordan.

The bigger agenda on a military coalition against IS requires an invitation from the central government in Baghdad, even to arm Kurdish forces.

The most important Nato summit in decades. It is a measure of the world's new instability that President Putin himself attended the last Nato summit in Chicago in 2012. And the main agenda here in Wales is dealing with chief summit guest from two years ago.